Method of torque modulation

ABSTRACT

A control method for modulating the torque in an internal combustion engine with mechanical power transmission and with pneumatically, hydraulically or electromagnetically controllable valves that are open and closed based on signals from a control system, by which method a torque that is requested in an operative situation at a certain moment is provided by a selection of the frequency with which power strokes are performed by controlling the number of power strokes in relation to the number of idle strokes. The power strokes take part in 2-stroke cycles or 4-stroke cycles, and one or more 2-stroke cycles are alternated with or more 4-stroke cycles.

TECHNICAL FIELD

The present invention relates to a control method for modulating thetorque in an internal combustion engine with mechanical powertransmission and with controllable valves. The control method meets, ina new way, a varying need of torque, in a way that reduces the fuelconsumption and the environment affection in relation to previouslyknown methods.

The invention is applicable to internal combustion engines with varyingload, for example Otto, Diesel or Wankel engines that are used fordriving vehicles, aeroplanes, boats, ships etc. In order to make itpossible to take advantage of the invention, the engines must beequipped with controllable valves.

The invention can only be reduced to practice through the use of anelectronically based control system. The software in the control systemdetermines the function thereof. The software that is used forimplementing the invention may, for example, be applied as a part of alarger control system that may also bring completely other properties tothe engine in question.

BACKGROUND OF THE INVENTION

During recent years, it has been possible to develop internal combustionengines towards an improved operation economy and a reduced environmentaffection by the introduction of digital control systems foroptimization in different operative situations. For example, this is thecase for fuel injection, ignition, variable compression and controllablevalves.

During the powering of vehicles it is a problem that, in spite of saidimprovements during the recent years, the varying operative situationsresult in the average efficiency of the engines becoming low and theeffect on the environment becoming large. There is a further problem asthe varying operative situations also result in a varying composition ofdifferent poisons and pollutions of the exhaust gases, thereby makingthe filtering of exhaust gases difficult.

One example of a vehicle engine that is environment friendly is thehybrid engine that mainly operates at a constant number of revolutionsper minute that is adapted to a predetermined generator. This engineoperates as best when it performs the requested operation at the highestpossible efficiency. As the load is constant, also the combustion can beset in order to, in combination with different techniques, result in thelowest possible content of pollutions and poisons in the exhaust gases,such as for example nitrogen oxides and hydrogen carbons, and, incertain cases, soot particles.

If internal combustion engines could meet a varying need of torque,which is the result of different operative situations, with the highestpossible efficiency, from the lowest need to the uppermost need,important advantages as to operation economy and environment would beachieved. Such an engine would have the advantages of the hybrid enginein the different operative situations that may come in question for avehicle. The free-piston engine, based on the idea of performing optimalpower strokes upon need thereof, and only then, would be a solution tothe above-mentioned problem. However, the free-piston engine in whichthe moment of the piston is controlled by means of hydraulics orpneumatics, has not become widely spread since there has not beendeveloped a sufficiently good solution for controlling the piston duringthe compression stroke with subsequent combustion. Strongly acceleratingincrease of pressure at the end of the compression stroke, and an added,explosive increase of pressure during combustion, results in problemswith controlling the movement of the piston at its upper dead point.

The present invention implements, to a high degree, the advantages ofthe free-piston engine, and solves the above mentioned problems.

THE OBJECT OF THE INVENTION

The object of the present invention is to present a new control methodconcerning the modulation of the torque in internal combustion engineswith mechanical power transmission and with controllable valves, inorder to solve set problems and provide said advantages.

SUMMARY OF THE INVENTION

The object of the present invention is achieved by means of a controlmethod for modulating the torque in an internal combustion engine withmechanical power transmission and with controllable valves,characterized in that a torque that is requested at a certain moment ofoperation, is provided by the selection of the frequency with whichpower strokes are performed. Further features are disclosed in thefollowing description and in the patent claims.

Mechanical power transmission is referred to as that the energy in amass of gas that expands after combustion is transmitted to a crankshaftor any other rotating shaft.

Controllable valves are referred to as valves of the combustion chamberof an engine, said valves being able to be opened and closed based on asignal from a control system.

Power stroke is referred to as a stroke in which the energy of a mass ofgas that is expanding after combustion is transformed to mechanicalwork. The power strokes may be optimal or normal, as in today's engines.

Here, idle stroke is referred to as a stroke in which there is no gasexchange, and no supply of air or combustion, and in which, thereby,there is no positive work being performed during what would otherwisehave been a power stroke. This results in a minimum of friction and heatlosses. During an idle stroke, no air, or air and remaining fuel ispumped through the engine. An idle stroke requires that at least theinlet valves are controllable, in order to be kept closed for thepurpose of preventing air from being introduced until they are opened;however the invention is as most advantageous if also the outlet valvesare controllable.

The power stroke frequency may vary between 0 and 100 percent of therelevant number of revolutions per minute of the engine. A frequency canbe selected by determining that a power stroke shall be performed everyn revolution, the remaining strokes being idle strokes, or, for example,by determining that power strokes are to occur according to a series inwhich an idle stroke is introduced each n revolution. During vehicleoperation, it is the driver that, by means of gassing, indicates theneed of and request of torque. The gas application is registered by asensor that makes the control system choose the frequency with which thepower strokes are performed.

Here, an optimal power stroke is referred to as that the work that isperformed during the power stroke, with regard to the relevanteconomical and environmental and further practical conditions, is aslarge as possible in relation to the amount of fuel that is consumed forthe work. By meeting the demand of torque at every moment by means of afrequency of optimum power strokes, the best possible operation economyis achieved.

At a 4-stroke cycle operation, the optimum power stroke results in thepossibility of closing the inlet valves early in relation to what iscommon in contemporary engines, and that the outlet valves can be openedlate in relation to what is common. Accordingly, the cycles according toMiller and Atkinson respectively becomes naturally present. By means ofengine experiments, it is possible to test which settings thecontributing parameters and the control values should have at eachnumber of revolutions per minute of the engine. Alternatively, thecontrol system may be adaptive, i.e. self-taughting.

An optimal power stroke during 2-stroke cycle operation differs from anoptimal power stroke during 4-stroke cycle operation in that thecylinder pressure that exists when the outlet valves open is to be takenadvantage of for the purpose of performing an exchange of gas. Rapidlyopening outlet valves results in a pulse of out-flowing exhaust gasesthat create under pressure, an absolute pressure below 1 atmosphere, inthe cylinder. The outlet valves are closed, and the inlet valves areopened in such a time-relationship to the closure of the outlet valvesthat the under pressure can be taken advantage of in an optimum way inorder to provide the correct mass of air before the followingcompression stroke and subsequent power stroke. Optimal power strokescan also be performed by the use of outlet ports that are released inconnection to the lower dead point of the piston.

During the 2-stroke cycle operation, a scavenging pump can be used inorder to fully, or partly and then in combination with an under pressurein the cylinder, execute the gas exchange. However, the use of ascavenging pump results in a lower efficiency than what is obtained withthe above mentioned, optimal power stroke.

At certain operation conditions it might be necessary to abandon the useof optimal power strokes, for example when maximum effect is needed orif there are enforcing demands.

An engine, and the control system thereof, can be construed for morethan one optimum power stroke frequency at a predetermined rotationspeed of the engine, by enabling the use of two or more types of fuelthat, due to their properties, result in the existence of a plurality ofoptimum power stroke frequencies. Fuels like petrol and ethanol are oneexample of such a combination. At each rotation speed there is oneoptimum power stroke for petrol and another optimum power stroke forethanol.

According to the invention, the systems for supply of air and fuel areset in such a way that, at each power stroke, at a predetermined numberof revolutions per minute of the engine, the same masses of air and fueland the same mixture of air and fuel shall be ignited as in the otherpower strokes within the relevant number of revolutions per minute ofthe engine. Further, any possible EGR is the same for different powerstrokes. As the preconditions for the combustion are repeated and allthe time the same, the result is that each power stroke, at apredetermined rotation speed, will develop the same amount of work asthe others, and that the composition of the chemical compounds of theexhaust gases remain the same, thereby improving the possibilities forexhaust gas filtering.

In common 4-stroke cycle internal combustion engines the combustion,during work of the engine, takes place every second revolution, and in2-stroke cycle engines every revolution. The systems for gas exchange ofthese engines are unsuitable since the result thereof is that air andthe remaining fuel, for example non-combusted hydrocarbons, are pumpedthrough the engine, which requires counter work and puts a load on theenvironment. In order to be able to use the invention, with theadvantages that can be achieved, valves or ports for gas exchange mustbe possible to close when one or more power strokes are not to beperformed, but when, instead, one or more idle strokes are to beperformed, which is an often upcoming situation at partial loads.Accordingly, the invention prerequisites controllable valves, at leastcontrollable inlet valves.

With controllable valves, where the time of opening and closure of thevalves is controlled by a digital control system, with sensors for,among others, piston positions and number of revolutions per minute, andwith electronics and software belonging thereto, gas exchange and powerstrokes can be performed only when needed. The remaining time thevalves, at least the inlet valves, are kept close. This means that, foreach requested torque, within the range of performance of the engine atoptimum power strokes, the frequency of optimum power strokes that meetsthe relevant need of torque can be selected.

The control method implies that a digital control system senses acertain and momentary need of torque. If this need is within the rangethat can be provided by provision of optimum power strokes, a certainfrequency, the one that is assumed to meet the need in question, isselected by the control system. At a certain number of revolutions perminute, the power strokes generally result in the same amount of workeach time that they are performed. Thereby, it is the frequency of powerstrokes that is decisive for the size of the torque.

By means of controllable valves, the supply of air and fuel, and theremoval of exhaust gases, gas exchange, can take place immediatelybefore and after the power strokes. In order to be able to select afrequency that results in one power stroke being executed eachrevolution, also gas exchange has to take place each revolution, as in a2-stroke cycle engine. Gas exchange may also take place as in today's4-stroke cycle engines, i.e. a suction stroke is introduced, with theresult that a power stroke only can be performed each second revolution.Accordingly, the invention implies that a need of a certain torque canbe met through a selection of a frequency of 2-stroke cycles or 4-strokecycles or a frequency in which one or more 2-stroke cycles are mixedwith one or more 4-stroke cycles. The invention implies that differentfrequencies of power strokes can be selected for different enginecylinders. If the inlet valves, but not the outlet valves, arecontrollable it is only possible to perform 4-stroke cycles.

The control system is provided in order to, as an answer to a torquerequest, concerning increase or decrease of the torque, from a driver,for example via the gas pedal in a conventional way or in any other way,control the relation between the number of power strokes in relation tothe number of idle strokes of the engine based on the requested torque.The control is not performed by bringing individual cylinders of theengine out of function, but by a variation of the relation between thenumber of power strokes and the number of idle strokes for eachcylinder, and by having different relations for different cylinders. Thecontrol system provides for this by the opening and closure of inletvalves and outlet valves to the combustion chamber of the respectivecylinders, or by the opening and closure of at least the inlet valves,should the outlet valves not be controllable. The opening and closure ofat least the inlet valves and in the relevant cases also the outletvalves, is thus performed based on the torque requested by the driver.The activation takes place by means of control signals from a controlunit of the control system. At least the inlet valves, but in therelevant cases also the outlet valves, are, for example, pneumatically,hydraulically, electromagnetically or in any other way activated valves.Controllable valves are referred to as such activated valves. If theoutlet valves are not controllable, the power strokes will always takepart in 4-stroke cycles. If, however both the inlet and the outletvalves are controllable valves, the control system may be arranged inorder to, at given conditions, change between 4-stroke cycles and2-stroke cycles for the cylinders of the engine. For example, onecylinder may operate with 2-stroke cycle and another one with 4-strokecycle. A maximum torque is obtained if each cylinder operates with2-stroke cycle each revolution, i.e. when there are no idle strokes.Theoretically, 2-stroke cycles are the most economical ones, and if thatwould be the case also in reality, the suction stroke of the 4-strokecycle is only needed upon the start. The control system can be arrangedin order to calculate if, and under what conditions 2-stroke cycle or4-stroke cycle is the most economical one, and thereafter select the oneto be performed with a certain frequency. Accordingly, the controlmethod includes controlling the operating cycles of the engine to be2-stroke or, if there are more than one cylinder, and/or 4-stroke basedon these given conditions. A control system comprises a control unitthat includes a computer program adapted for this purpose and providedon a data carrier. The control unit is operatively connected to acircuit for pneumatical, hydraulic, electromagnetic or other type ofactivation of at least the inlet valves, but in certain cases also theoutlet valves. The control unit may, for example, be arranged to controlmagnet valves by electric signals, said magnet valves being arranged inthe circuits for the activation of the inlet valves of the engine or theinlet and outlet valves of the engine. The control unit is operativelyconnected with the members for torque request, for example a gas pedalvia which a driver gives an order regarding the requested increase ordecrease of the torque of the engine. The control system for a frequencymodulated torque may constitute a subsystem, for example an economymode, in a larger control system that may also bring completelydifferent properties to the engine in question.

There are great advantages of spark ignition engines by which the gasapplication today is regulated by means of a throttle. By throttleregulation the compression relationship is not optimal at any otheroccasions than at a high gas application. Throttle regulation results inthrottle losses. A regulation by means of controllable inlet valves willalso result in throttle losses, but they will be significantly smallerthan by throttle regulation. The application of the present inventionwill result in non-existence of throttle losses caused by a throttle,and that throttle losses will be minimized upon use of controllableinlet valves. Diesel engines do not have any throttle regulation, and,therefore, the advantages of the invention are less in this case, but itis known that the utilizing of the fuel can be improved by an earlyclosure of the inlet valves. The formation of relatively high contentsof nitrogen oxide and soot are well known problems by diesel engineoperation. The present invention also gives a possibility of varying thetorque for diesel engines by, especially at idle operation and lowloads, repeating an operating setting that result in a high efficiencywhile, at the same time, the generation of soot and nitrogen oxides isminimized, which is of significant advantage. The advantages of theinvention in connection to diesel engine operation become more evidentif the turbo aggregate is provided with variable geometry, so calledVGT. Homogenous Combustion Compression Ignition, named HCCI, is acombustion cycle with high efficiency and other environmentaladvantages, but with a low effect density. The problem of HCCI ariseswhen a varying demand of torque is to be met. There still has not beensuggested any control method in which said advantages can be maintainedupon varying load. However, the invention implies a control method forvarying the load and maintaining the advantages of HCCI. However, theadvantages of the invention will be greater if the HCCI-engine isequipped with exhaust gas recycling, so called EGR, which permits asubstantially increased effect density. Accordingly, the presentinvention is of great value for the combustion cycle of HCCI.

When the invention is applied to a vehicle with a traditional drivingline, the forward movement of the vehicle may be experienced as somewhatirregular at low speed. In order to avoid this, the control system may,for example, be arranged such that, when the speed or the number ofrevolutions per minute goes below a certain value, it controls theengine to change from optimum power strokes to semi optimal powerstrokes in order to increase or maintain the frequency of power strokes.However, this is not any problem when the gearbox or the transmission isin an idle position. A system with a hydraulic driving line would alsoresult in the non existence of said problem. In such a driving line, anengine with the invention applied thereto may pump hydraulic oil to anenergy storage, whereby an uneven operation at rotation speeds does notmatter. The vehicle is driven under a regular tap off from the energystorage.

The lower load extraction, the greater saving of fuel and otherenvironmental advantages are obtained with a frequency modulated torque.An engine and its control system may be designed in order to cover thewhole operative range of the engine with different frequencies ofoptimal and semi optimal power strokes as the only control method. Thiswould give the engine a very good fuel economy within its wholeoperation range.

The invention is not departed from by the selection of power strokesthat are not optimal or by selecting a frequency that is not the bestone.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exemplifying, schematic picture showing a cylinder with apiston 1. The piston is moving during a suction stroke in a 4-strokecycle, and air is flowing together with fuel through the open inletvalve 2. The inlet valve 2 and the closed outlet valve 3 are constitutedby controllable valves. A circuit 4 is used for activation of thevalves. A control unit 5 is operatively connected to the circuit 4 forsignal control of the circuit and the valves connected with the circuit.A member 6, for example a gas pedal, is operatively connected with thecontrol unit 5 for torque ordering. A sensor 7, at a graduated ark thatis mounted on the engine shaft 8 and operatively connected with thecontrol unit 5, repeatedly gives information to the control unit aboutnumber of revolutions per minute and position of the piston in thecylinder 1. The control unit 5 decides when the controllable valvesshall open or close, and, thereby, the frequency.

1. A control method for modulating the torque in an internal combustionengine with mechanical power transmission and with pneumatically,hydraulically or electromagnetically activatable, controllable valvesthat are opened and closed based on signals from a control system, bywhich method the torque required in an operative situation at a certainmoment is provided by a selection of the frequency with which powerstrokes are performed by controlling the number of power strokes inrelation to the number of idle strokes, wherein, the power strokes takepart in 2-stroke cycles and 4-stroke cycles, and wherein one or more2-stroke cycles are alternated with one or more 4-stroke cycles, saididle strokes being performed without any introduction of air into thecombustion chamber after the nearast foregoing power stroke.
 2. Acontrol method according to claim 1, characterized in that the enginecomprises a plurality of cylinders, and that the power stroke frequencyis chosen such that it is different for different cylinders.
 3. Acontrol method according to claim 1, characterized in that the powerstrokes are optimal.
 4. A control method according to claim 1,characterized in that, at each power stroke, at a certain rotation speedof the engine, generally the same masses of air and fuel, and generallythe same mixture of air and fuel is ignited as in the other powerstrokes.
 5. A control method according to claim 1, characterized in thatthe composition of the different chemical compounds of the exhaust gasesremain generally the same.
 6. A control method according to claim 1,characterized in that the power stroke frequency at a given rotationspeed of the engine is decisive for the torque.
 7. A control methodaccording to claim 1, characterized in that it comprises the use of acomputer program that, by means of signal control, based on a torquerequested by a driver, chooses the frequency of power strokes.
 8. Acontrol method for modulating the torque in an internal combustionengine with mechanical power transmission and controllable valves openedand closed based on signals from a control system, comprising the stepsof: providing torque required in an operative situation by selecting afrequency with which power strokes are performed, the selection bycontrolling a number of power strokes in relation to a number of idlestrokes, the power strokes taking part in 2-stroke cycles and 4-strokecycles, and one or more 2-stroke cycles are alternated with one or more4-stroke cycles, the idle strokes being performed free of anyintroduction of air into the combustion chamber after the latestforegoing power stroke.
 9. A control method for modulating the torque inan internal combustion engine with mechanical power transmission andcontrollable valves opened and closed based on signals from a controlsystem, comprising the steps of: providing torque required in anoperative situation by selecting a frequency with which power strokesare performed, the selection by controlling a number of power strokes inrelation to a number of idle strokes, the power strokes taking part in2-stroke cycles or in 4-stroke cycles, and one or more 2-stroke cyclesare alternated with one or more 4-stroke cycles, the idle strokes beingperformed free of any introduction of air into the combustion chamberafter the latest foregoing power stroke.